Pressure compression mould for the production of tires

ABSTRACT

The pressure compression mould for the production and/or revulcanisation of tires forms a hollow space where the pressure and the temperature can be regulated. Each sidewall of the compression mould is designed with an elastic and flexible annular disc membrane which the sidewalls of a tire placed in the mould is made to thrust against in order to control the outwardly directed tensile forces in the tire. The membrane sides facing towards the mould hollow space is equipped with an annular disc-shaped membrane-protective plate in order to prevent direct contact between side faces of the tire and the respective membranes during the production/vulcanisation. The plate is split up, both in the radial and circular plane, into a series of smaller plates the free ends of which mutually overlap each other. When a tire is placed in the mould and the mould hollow space is pressure set, the sides of the tire are pressed outwards towards the plates which flex afterwards and furthermore the membrane is flexed outwards and is stretched. Direct contact between the membrane and sides of the tire is avoided so that the sides of the tire are not vulcanised fast in the membrane.

The present invention relates to an arrangement in the production ofair-filled tires.

More specifically the present invention has to do with apressure-compression mould, that is to say a vulcanisation mould, forthe vulcanisation of tires.

The present invention has especially to do with the last step, that isto say the vulcanisation step, during the production of tires, andrelates particularly to the reuse of old worn down tires during theutilisation of a recapping or tread application process.

When the wearing surface of a tire is worn down, for example downtowards the pattern depth which the authorities accept, the tire can beused again on recapping or applying a tread.

On recapping, the tread is completely ground away. That is to say thatall the old design is completely removed down to fresh rubber andwithout damaging the cord in the casing. A portion of the old rubber onthe sides of the tire can also be removed. By dissimilar techniques, anew unvulcanised tread can be applied. On the sidewalls there can alsobe deposited a thin layer of unvulcanised rubber. After the tread isapplied, a flexible tube can be placed inside the tire, if desired thevulcanisation mould comprising a bellows or being tubeless. The mould isheated in advance to about ca. 150°-170° C. by conducting heated steamthrough ducts in the mould, if desired the mould being heated byelectrical resistance heating. When the raw tire is heated and ispressed out at the same time against the walls of the mould by supplyingan internal pressure, the newly applied rubber material in the tire ismoulded and vulcanised, the rubber mixture being converted from amouldable plastic material to a solid elastic material.

Vulcanising is the description of the chemical reaction which occursbetween the rubber material and sulphur under the influence of hightemperature and pressure. The time which is needed to complete thevulcanisation process is dependent on both the pressure, temperature andthe thickness of the rubber during vulcanisation. During the day'sautomobile tire production, zinc oxide, stearic acid and other compoundswhich accelerate the vulcanisation are also added to the rubber mixture,besides sulphur.

Based on the above, there can also be used, for recapping automobiletires, factory-ready treads which are adapted for the different tiredimensions and breadths and which have a finished design and are readyvulcanised. On the finished worn down tire casing, a thin layer ofunvulcanised bonding rubber is first placed, and on the outside there isdrawn a sleeve (envelope). The vulcanisation itself takes place byputting the entire tire in an autoclave where it is supplied withpressure and it is heated to a temperature of ca. 98° C. Since the treadis vulcanised in advance it is only the bonding rubber which is to bevulcanised. This method is mentioned in U.S. Pat. No. 3,839,123.

When a tire is recapped thus by a heat vulcanisation as is indicatedabove, it is really the last step of the new tire manufacture which isrepeated whereby the tread is renewed.

Even if the dimension designations and the diameters on thereconstructed tires are correct relative to the metal mould which thetires are to be vulcanised in, the volumes of the tires can bedissimilar as a consequence of variations in the length and shape of thesidewalls of the tires.

Thus, if the sidewalls of the vulcanisation mould do not agree with thesidewalls of the tire or the tire volume in this side portion, anundesirable deformation of the tire will arise during the vulcanisation.If the mould for example is dimensioned for a greater tire volume thanthe tire which is to be recapped, significant tensile forces will arisein the cord casing beyond those designed to be withstood. The danger isthereby great for permanent deformation of the tire to occur. Thisdisagreement in volume between the side surface portions of the tire andthe manufacturing mould leads to unfortunate deforming flows of therubber material during the pressing.

This problem can be solved, as for example is known from DE patentpublication 2,038,878, by making the sidewalls of the tire thrustagainst a flexible and elastically annular disc-shaped membrane which isarranged on each side of the sidewalls of the mould. Furthermore themembrane acts against an external annular groove-shaped hollow spacewhich is recessed in the mould in which there is established a givenfluid pressure, where the fluid can be for example air, P2, and themembrane will thus close accurately to the length and shape of the sidesof the tire. During the vulcanisation step the pressure P2 is regulatedin the hollow spaces so that the pressure here is lower the whole timethan the pressure P1 in the hollow space of the mould.

With this vulcanisation mould tires which are both large and small canbe vulcanised in the same mould, there being achieved a controlledtension in the sidewalls of the tire and one avoids the tire beingexposed to damage from deformation.

With the arrangement is achieved limiting outwardly directed movement inthe sidewalls by the cord construction of the tire, while the metalportion of the mould determines the remaining shape of the tire.

The disadvantage with this vulcanisation mould is that unvulcanisedrubber, in the region which borders the membrane, does not get thedesired outward flow and finish in connection with the vulcanisation.Besides the membranes have a tendency to vulcanise firmly in theunvulcanised rubber which is applied to the sidewalls of the tire beforeplacing in the mould.

The object of the present invention is to provide an arrangement withwhich the afore-mentioned disadvantages in manufacture and recapping oftires can be eliminated.

The object of the present invention is to also fashion the portionswhich bear against sidewalls of the tire by a metallic material as inthe remaining metal matrix.

Briefly, the invention is directed to a vulcanizing mould for a tirecomprising a pair of mould halves defining an annular hollow space toreceive a tire with each mould half having an annular cavity facing theannular space. In addition, a pair of annular elastic membranes areprovided with each membrane being mounted over a cavity in a respectivemould half to define a closed annular hollow space.

In accordance with the invention, a plurality of flexible non-elasticplates are mounted over each of the membranes in facing relation to thehollow space in order to face a side wall of a tire in the hollow spaceand thereby prevent contact between the tire side wall and a respectivemembrane. As such, the flexible non-elastic plates serve as protectiveplates to prevent the side wall of a tire being subjected to avulcanizing process coming into contact with the flexible elasticmembrane. In addition, the plates on each membrane are disposed inoverlapping relation to each other in order to accommodate flexing ofthe membranes during a vulcanizing process.

In the following description the invention will be explained furtherwith reference to the accompanying drawings, in which:

FIG. 1 shows a cross-section through a tire.

FIG. 2 shows a cross-section (that is to say the one half) of avulcanising mould according to the present invention.

FIG. 3 shows an enlarged section of the left half of the vulcanisationmould according to the invention.

FIG. 3a shows an enlarged section of the mould in order to illustratehow the plates which during the vulcanisation are to be arranged betweenthe tire sidewall and the membrane, are fastened in the mould.

FIG. 4 shows in a radial section the membrane protective plates in orderto illustrate how the plates can be arranged in overlappingrelationship, according to an embodiment of the invention.

In order to better explain the significance of the present invention,the following will comprise a summing up of constructions of dissimilartires. With reference to FIG. 1 a tire consists of a tread 11, shoulder12, sidewall 14, a tire foot 16 with a tire toe 18, tire heel 20, wirecore 22, together with cord casing 24, protective layer/breaker/belt 26plus a sealing layer 28 when the tire is tubeless.

An automobile tire is in principle a receptacle for compressed air. Itis the air which carries the load which the wheel is exposed to. Thetire's own rigidity is insignificant in relation to the load it shallcarry, something one sees if one is unlucky enough to have apuncture--the tire collapses instantly.

A diagonal tire consists in principle of three main portions, tread,textile skeleton and tire foot.

The unvulcanised tread is produced on a so-called tuber which operatesaccording to the same principle as a mincing machine. The tread rubberis forced by means of a screw out through a mouthpiece which gives thetread a specific profile all according to which dimension it is to beused for. The tread passes thereafter through a cooling plant, is cut upinto specific dimensions and is controlled as to quality and weight.

The rubber of an automobile tire tread and of the sidewalls of the tireusually consists of two dissimilar mixtures. The tread of the tire whichlater comes makes contact with the road, shall have properties whichprovides high wear strength. The rubber on the side, which is to formthe sidewalls of the tire, shall first and foremost tolerate theconstant flexing which the sides of the tire are exposed to. Thepreparation of these different rubber mixtures takes place in the tuberplant.

The casing is constructed of cord which are threads which consist ofsteel, nylon, rayon or other fibres.

Before the cord is built into the tire, it is covered with rubber. Thisis carried out by pressing the threads, together with the rubbermixture, between steel rolls in a calender which is a machine forsmoothing and pressing. It is very important that the rubber penetrateswell in between the cord threads so that each thread becomes wrapped inrubber. Otherwise the threads will gradually be able to be rubbed inpieces at the points of intersection. The covered cord will later be cutup into specific breadths at a specific angle.

The third main component of the tire is the tire foot. Several differenttypes of tire foot are used, but common to them is that they consist ofsteel threads which are covered with a layer of brass (copper/zinc). Theindividual threads are collected for a thread core where the number ofindividual threads can vary in breadth. The thread core is covered withrubber, after which it is spun up on a steel wheel the diameter of whichis dependent on the tire dimension the thread is to be used for.

In a diagonal tire the casing consists of two or more layers of cord.The innermost layer is laid so that the threads extend obliquely overthe tire at a specific angle to the centre line of the tread, usuallyca. 32°-36°. The next layer is laid so that the threads cross thepreceding layer and form the same cord angle with the centre line of thetread.

A radial tire is constructed and built up in another way from thediagonal tire. In the casing of the tire of a private automobile, rayoncord is usually employed, while belt layers of steel cord are employed.In truck tires, steel cord is employed both in the casing and in thebelt layers. In the radial tire, the cord threads of the casing form anangle of ca. 90° with the centre line of the tread. The radial tire isbuilt up with one or two layers in the casing. Between the tread and thecasing of the tire there is placed a rigid belt. This belt consists of2-4 layers of cord. The cord layers are laid so that the individual cordlayers form an angle of 15°-20°.

A diagonal belt tire is a combination of a diagonal and a radial tire.The cord angle on the diagonally constructed casing is about 40°.Between the casing and the tread of the tire there is placed astabilising belt with an angle of ca. 20°. This type of tire is producedmostly in the U.S.A. where it has the designation "Bias belted", whileit is little used in Europe.

The vulcanisation mould according to the present invention is used ontires of the type which are illustrated in FIG. 1, and which arereferred to in the introduction of this specification.

The vulcanisation mould 30 (that is to say really the matrix of avulcanisation machine) is illustrated schematically in FIG. 2. The mould30 comprises two mould halves 32a, 32b which form an annular mouldhollow space 34 wherein the tire 10 which is to be vulcanised ismounted. In each of annular sidewall mould portions 36a, 36b of thevulcanisation mould there is formed a continuous circular cavity. Anelastic and flexible membrane 38a, 38b formed as an annular disc, isarranged over the cavity. In this way, there is formed a closed annularhollow space 40a, 40b, one on each side of the mould hollow space 34,and each of these is defined by the sidewall mould portion and themembrane. The membranes 38a, 38b can according to one embodiment bepressed into the annular groove in the metal material in the respectiveinner 42 and outer 44 surfaces of the mould portions 36a, 36 b andfastened in a suitable manner. As shown in FIG. 2, protective pairs ofmetal plates 66, 68 are placed behind and against each membrane 68a, 38brelative to the hollow spaces 40a, 40b. Referring to FIGS. 2 and 3a, themost preferred solution to mount the membrances 38a, 38 b is to mountboth the membrane 38 and and plates 66, 68 to the mould material at 42(and 44) by installing and fixing their peripheral fastening edges in ahook-shaped formation 80 (FIG. 3a) of the mould. The fixing can be doneby tightening an annular clamping ring 82, for example of metal, intowards the hook formation 80 over the membrane 38 and the element 66,68 which are thereby clamped fast. The clamping ring 82 is designed sothat it forms together with the portions of the mould, uniform surfacetransitions against the tire. With such a fastening solution, membranesand protective plates can be readily released and taken out when theyhave to be replaced or repaired. The border lines drawn in on FIGS. 2and 3 between the mould halves 32a,b and between the sidewall mouldportion 36a, 36b and the mould halves 32a,b are to illustrate that theseapparatus parts of metal can be mutually displaced in parallel and beseparated relative to each other in order to install in or take a tireout of the mould. The apparatus according to FIG. 2 really constitutesthe inner matrix portion of a greater vulcanising machine, where for onething there are designed in the external machine parts (which are notshown in the Figure) ducts for steam having higher temperatures in orderto heat up the vulcanising rubber.

The membranes have a breadth which corresponds in height to sidewalls14a, 14b of the tire 10, and have a suitable thickness. The membranescan be made of a partially elastic, plate-formed material, and arepreferably of a rubber material. The protective plates can have a smallthickness since they are not exposed to tensile forces. Thus, thethickness can be from 0.1 millimeter and up to 5 millimeters, and athickness of ca. 1.0 mm will normally be well suited depending upon whatone finds most appropriate for the dissimilar plate materials and tiredimensions.

Referring to FIG. 2, a means is also provided for regulating thepressure in the mould hollow space 34 relative to the pressure in thetwo peripheral annular hollow spaces 40a, 40b. This means includes apump 46 and respective conduits 54, 58, 60 which communicate with therespective hollow space 34 and annular spaces 40a, 40b to deliver apressurized medium thereto.

With the pump 46 fluid can be conducted from a source 48 through aconduit 50 to a branching point 52 from which the first conduit 54 leadsin to the mould hollow space 34, while a second conduit 56 is furtherbranched into the two conduits 58, 60 which lead in to the respectiveouter annular spaces. When a tire is to be vulcanised, it is placed inthe mould as is illustrated by the broken line in FIG. 2. Fluid (in theform of air) is pumped into the mould hollow space 34 to a pressure P1while the outer peripheral ring spaces 40a,b are pressure set to apressure P2. By adjusting a control valve 62 the pressure is mutuallyadjusted in the two circuits so that the mould hollow space pressure P1is higher than the annular space pressure P2. Thereby, as a consequenceof the excess pressure, sidewalls 14 of the tire will be flexed outwardsand thrust against the membranes. When the vulcanisation is complete thepressure relief from the hollow spaces occurs via a discharge valve 64.

According to the invention, vulcanisation of the membrane 38 fast to thesides of the tire is avoided by arranging the pairs of annulardisc-shaped plate elements 66, 68 on the inside of each membrane, thatis to say in towards the mould hollow space 34. Reference is also madehere to FIG. 3 which illustrates an enlarged section of the mould ofFIG. 2. Each pair of plate elements is split up in the circular planeinto two annular disc plates 66a, 68a where the one annular disc plate66a is fastened at outer diameter 42 of the mould, while the otherannular disc plate 68a is fastened at the inner diameter 44 of themould. The annular disc plates are preferably split up in the circularplane so that the inner peripheral edge 70 of the annular disc plate 66awhich is fastened to the outer periphery 42 of the mould, overlaps theouter peripheral edge 72 of the annular disc plate 68a which is fastenedin the inner periphery 44 of the mould. In addition to the splitting upin the circumferential plane with overlapping, the plates are also splitup and overlap each other in the radial plane. On operation of theapparatus the plates also become situated between the rubber membrane 38and the external side wall 14 of the tire.

According to an alternative solution, the radially split up plate 66aextends from the outer periphery 42 (FIG. 3) and completely down to theinner periphery 44. In this instance the free lower edge of the plate66a will, on operation of the apparatus, slide between the tire and themetal material of the mould. Alternatively, the radially split up innerplate 68a can have such a design where it projects completely up to theouter periphery of the mould. In such an instance a construction ispossible where the split up protecting plate only partially stretchesover the membrane.

It is also possible that there are certain portions of the tire notneeding to bear against a protecting plate, that is to say that it canmake direct contact with the membrane 38a.

According to a further construction the plates can only be fixed above(alternatively below) and lie free in a groove below (alternativelyupper) where they are largely freely movable.

The splitting up of the annular disc plates is more clearly evident fromFIG. 4 which shows a plan view in a direction outwards from interior 34of the mould and shows outer 42 and inner 44 "diameter" of the mouldplus the annular disc-shaped protecting plates 66a, 68a. The plates inthe circular plane are split up into two plates, as explained inconnection with FIG. 3. Furthermore, in the radial plane, both the outerplate 66a and the inner plate 68a are split up into a number of smallerplates, such as 8 plates as is illustrated by A-H for the outer plate 66(one shall not be tied to the construction with 8 plates which isillustrated in FIG. 3). The full lines show one visible edge of eachpart plate (A-H), while the dotted lines show the one end edge whichlies overlapping and concealed under the next plate in the series. Thusfor example the one visible end edge of the plate A lies at 72 while theother end edge 74 lies under the next plate B in the series.

As is illustrated in FIG. 4 the radial splitting up of the interiorplate is displaced relative to the radial splitting up of the exteriorplate. This is done so that the plates shall not impede one another'smovements during the use of the apparatus. For example the thrustingagainst each other of edge portions of the plates is avoided during saidmovement of the plates.

While the membrane is formed of an elastic and flexible material, suchas rubber, the plate-shaped membrane-protecting elements 66a, 68a aremade of a non-elastic material, but bendable (less rigid) material. Aplate material of metal or plastic will be well suited. The platematerial is preferably made of metal, and especially of aluminium orsteel. These metals exhibit low or no adhesion capability towardsvulcanising rubber.

When a tire 10 is mounted in the mould the outer side surfaces of thetire side walls 14 will consequently form an abutment against themembrane-protecting elements 66, 68. When the pressure in the mouldhollow space 34 increases to the necessary level above the pressure inthe annular spaces 40a, 40b, the tire sides 14 are pushed somewhatoutwards in order to try to reestablish the pressure equilibrium. Whilethe rubber membrane is flexed outwardly and is stretched as a result ofits elasticity, the protecting plates will only be flexed outwardly inthe same degree. But the plates will not be able to be stretched becauseof lacking the elasticity, and the respective outer and inner peripheraledges 70, 72 will then relatively speaking be mutually displaced each inits respective direction, sliding against each other. The plates aredimensioned with such a breadth that the end edges will not slide fromeach other during the outward flexing, and therefore there will not beformed any gap between the plates.

When the vulcanisation is complete, the pressure is relieved and thetire is taken out of the mould.

As a result of the protection plates of metal exhibiting higherrigidity, there is achieved the occurrence of a pressure balancingduring the vulcanisation when the membrane presses the protecting platestowards the tire sidewalls. There will arise a transport/outward flow ofthe uneven unvulcanised rubber from regions with higher abutmentpressure to regions with lower abutment pressure. In this way cuts orconcavities in the side faces of the tire will be filled up by flowablerubber material, and the side of the tire is smoothed out as a result ofthe tire impacting against a material which is more rigid than rubber.In addition the earlier problem with rubber material which vulcanisesfast in the membrane is avoided. The rubber material has as mentioned amuch lower adhesion to aluminium than to the membrane of rubber.

By the present invention there is consequently achieved a big advance inthe vulcanisation of tires.

I claim:
 1. Pressure compression mould for producing or revulcanizing oftires where the compression mould comprises separable mould halves whichcombined form an inner pressure- and temperature-regulatable annularhollow space adapted for arrangement of a tire, the mould halvescomprising respective sidewall mould portions,a part of each of thesidewall mould portions is formed with an elastic and flexible annulardisc membrane which on placing the tire in the mould, is adjacent to arespective outer tire sidewall, characterized in said sidewall mouldportions of the compression mould having a plurality of flexible andnon-elastic plates having a dimension such that the membrane sidesfacing towards the hollow space are largely covered by the plates, andadjacent plates having free edge portions arranged so that they mutuallyoverlap each other, whereby the plates prevent contact between the tireand the membrane.
 2. Pressure compression mould in accordance with claim1, characterized in that the plates overlap radially thereof andcircumferentially thereof.
 3. Pressure compression mould in accordancewith claim 1, characterized in that the plates are arranged in therespective outer and inner peripheries of the mould.
 4. Pressurecompression mould in accordance with any one of claims 1 to 3characterized in that the plates are formed by splitting up an annularplate element, in the circumferential plane, into respective annularouter and inner part plates, and the two part plates are further splitup in the radial plane into a series of outer plates and a series ofinner plates respectively, and each plate in the series overlaps thenext plate in the series, and that the plates in the respective outerand inner series mutually overlap each other.
 5. Pressure compressionmould in accordance with claim 4 characterized in that the radialsplitting up of the inner plate is displaced relative to the radialsplitting up of the outer plate.
 6. Pressure compression mould inaccordance with claim 4 characterized in that a plurality of the plateshaving a radially directed overlapping splitting up, extend from theouter periphery of the compression mould and completely down to theinner periphery of the compression mould so that the inner peripheraledge of the plate becomes situated between the tire and the material ofthe mould half.
 7. Pressure compression mould in accordance with claim 1characterized in that the plates are of a material which exhibits low orno attachment capability towards vulcanizing rubber.
 8. Pressurecompression mould in accordance with claim 7 characterized in that theplates are of a metal.
 9. Pressure compression mould in accordance withclaim 1 characterized in that the plates have a thickness in the regionof 0.1-5 mm.
 10. Pressure compression mould in accordance with claim 1further comprising said sidewall mould portions each having a pressure-and temperature- regulatable peripheral annular space where each saidmembrane defines a respective peripheral annular space separated fromthe hollow space, andmeans for regulating the pressure in the mouldhollow space relative to the pressure in the peripheral annular spaces.11. A vulcanizing mould for a tire comprisinga pair of mould halvesdefining an annular hollow space to receive a tire, each mould halfhaving an annular cavity facing said hollow space; a pair of annularelastic membranes, each membrane being mounted over said cavity in arespective mould half; and a plurality of flexible non-elastic platesmounted over each of said membranes in facing relation to said hollowspace to face a sidewall of a tire in said hollow space to preventcontact between a tire sidewall and a respective membrane, said platesbeing disposed in overlapping relation to each other to accommodateflexing of said membranes.
 12. A mould as set forth in claim 11 furthercomprises a first conduit communicating with said hollow space, a secondconduit communicating with said cavity in one of said mould halves, athird conduit communicating with said cavity in the other of said mouldhalves and a pump connected to each said conduit for delivering apressure medium thereto.
 13. A mould as set forth in claim 12 whichfurther comprises a branch conduit connecting said second conduit andsaid third conduit in parallel and a valve in said branch conduit toreduce the pressure of the pressure medium in each said cavity relativeto the pressure medium in said hollow space.
 14. A mould as set forth inclaim 11 wherein said plates are disposed in radially overlappingrelation.
 15. A mould as set forth in claim 11 wherein said plates aredisposed in circumferential overlapping relation.